F&B is overrated.
Now, with the Glyph of Conflag change, it's mainly picked up for the damage increase on Immolate.
The issue with that is that at 2000 spell power, it only increases immolates total damage by 300. Sort of a lackbuster imo.
I run the 40/31 with 5 Points in Demonic Tactics and a point in Conflagerate. My +SP is over 2300 with Imp and Fel Armor up, and my crit for Fire spells is over 35% with just imp and firestone. Considering my T7 proc on Incinerate, it usually crits around 40-45% of the time in a raid, without Boomkin Buff, Focus Magic etc. My DPS is around 4000, and it's super easy to use.